During the implantation of an endocardial lead body, the lead is introduced into the heart using a venous approach, usually from the subclavian or cephalic vein in the shoulder area under the pectoral muscle. To stabilize the lead body at the venous entry site, the lead body is secured to both the vein and to the surrounding fascia tissue. A suture placed around the vein near the lead entry point ties the lead body to the vein, and a suture sleeve around the lead body is used to anchor the lead body to adjacent tissue.
Suture sleeves in present use are generally tubular structures molded out of a soft, implantable elastomer such as silicone, and which are placed on the lead body during manufacture. After the lead body is implanted and tied to the vein, the sleeve is slid along the lead body to the location at which the lead is to be anchored to the underlying tissue. One or more sutures are then tied around the sleeve to compress it and thereby secure it to the lead body. Circumferential grooves in the outer surface of the sleeve are typically provided for this purpose. The last step is to anchor the sleeve to adjacent body tissue. Sutures may be passed through eyelets formed in a pair of tabs projecting from the sleeve which can provide the required anchoring; or sutures used to secure the sleeve to the lead body can also be used to secure the sleeve and lead body assembly to the underlying tissue.
In the design of suture sleeves, four (4) basic requirements should be met: (1) the sleeve should protect the lead body from high tie-down forces (for example, 6.5 lb. tie force) which might otherwise cause insulation or coil damage; (2) the slip force, that is, the force required to slide the lead body within the sleeve under wet conditions, should be greater than a predetermined minimum, for example, 0.7 lb, for relatively low tie-down forces (of, for example, 4 lbs.); (3) the slip force without the tie-down should be lower than a predetermined maximum, for example, 0.25 lb; and (4) the sleeve, before tie-down, should not fall freely on the lead body when the lead body is held or positioned vertically. These requirements should be met for a wide range of tie-down forces since the tie-down tightness varies among physicians and from implant to implant. And, in all cases, the sleeve must hold the lead body securely in position when tied-down.
The performance of suture sleeves is dependent upon several variables including the strength, elasticity and hardness of the suture sleeve material; the friction coefficient of the sleeve and the lead body; suture sleeve bore to lead body clearance; the stress distribution in the anchoring sleeve from the tie(s); and the strength of the lead body.
Tests have shown that for bipolar coaxial leads, suture sleeves with thick walls provide satisfactory lead body protection when tie-down forces are high. Such sleeves, however, cannot hold lead bodies securely in position under wet conditions (when the lead body is covered with bodily fluids, for example) with low tie-down forces. This is especially a problem with lead bodies coated with a lubricious material such as polyvinylpyrrolidone (PVP). On the other hand, when the wall thickness of the suture sleeve is reduced so that it can hold the lead in position at a low tie-down force under wet conditions, the sleeve is not always able to protect the lead body against insulation or coil damage when the suture tie is very tight.
Accordingly, it is an overall object of the present invention to provide a suture sleeve that reduces tie-down damage, yet holds the lead body securely in place for a wide, practical range of tie-down forces in implant conditions.
Another drawback of presently available suture sleeves is that at the time of lead revision, it is often difficult to locate the suture sleeve when it is encased in fibrous tissue. Present suture sleeves are translucent and are not readily visible to the physician because of lack of color contrast between the sleeve and the surrounding tissue. The physician is often forced to dissect tissue and search along the lead to locate the sleeve. Finding a suture sleeve is thus time-consuming, can be traumatic to the patient, and may cause damage to the lead body which can also make explantation difficult.
It would also be desirable to be able to fluoroscopically observe the suture sleeve so as to ascertain its position and the integrity of the portion of the lead body within the sleeve. Presently available suture sleeves, however, are not visible under fluoroscopy.
It is therefore another object of the invention to provide a suture sleeve that clearly contrasts with adjacent tissue and therefore is easily visible to the naked eye.
A further object of the invention is to provide a suture sleeve that is radiopaque for enhanced fluoroscopic visibility, yet not so radiopaque that the lead body's conductor coil(s) cannot also be seen fluoroscopically.